The present invention relates to a swage mount used to attach a magnetic head carrying arm in a magnetic disk drive unit. In particular, the invention relates to a method and apparatus for predicting twist out torque in a swage mounted head gimbal assembly of a magnetic disk drive unit.
There has been a continual drive to increase the storage density in magnetic disk drive units. This has been achieved in part by stacking magnetic disks in a "pack" all carried within the same disk drive unit. Each side of each disk has its own associated magnetic head used for reading and writing information thereon. Each magnetic head has its own associated support arm which positions the head above the disk surface. By moving the arm, the magnetic head moves between tracks on the disk surface. A servomotor is connected to the support arm opposite the head. The magnetic head is moved between tracks by activating the servomotor whereby the support arm pivots and the magnetic head at the opposite tip of the arm is swung between adjacent tracks on the disk surface. A linear actuator may alternatively be used to move a magnetic head. A linear actuator moves the head inward or outward on the disk along a generally straight line.
To further increase space savings in the disk drive unit, a single servomotor typically controls all of the support arms and their associated magnetic heads. Thus, all of the support arms are connected together and pivot about the same pivot point. This configuration is identified as an "E-block" (which refers to the shape formed by the adjacent arms and the servomotor/pivot assembly).
A common method of connecting a magnetic head to a support arm is known as "swaging" or "ball staking." This mounting method requires less vertical space than other methods, allowing disks to be stacked closer together, thus increasing storage capacity. In swage mounting two pieces together, a hollow tube which extends from one piece is placed inside a hole in a second piece. A rounded shape (the "ball") is forced through the hollow tube which causes the metal tube to expand and lock the two pieces together.
After manufacture, forces on the magnetic head may cause the swage mount to "twist out." To ensure reliable disk drive units, manufacturers set twist out specifications for the swage mount which must be met by all disk drive units. Manufacturers use a twist out torque test to check swage mounts. The twist out torque test is a destructive test in which a torque is applied to a swage mount connecting the magnetic head to a support arm. The torque required to permanently rotate the head by 0.1.degree. is measured. Since the twist out test is destructive, swage joints can only be tested on a sample basis. A low twist out torque indicates that the head might have rotated at a later time, causing the drive to fail. Furthermore, the testing procedure must be performed after the swage mount operation and cannot be performed in real time.